Because of the concern for environmental factors, previously known oil-containing metal working fluids require reclaiming or disposal other than by discharging them to common sewage treatment systems. In some cases the cost of disposal has become a major cost in that the cost of disposal approaches the initial cost of the fluid.
Metal working fluids fulfill numerous functions in various metal working applications. Typically, such functions include removal of heat from the work piece and tool (cooling), reduction of friction among chips, tool and work piece (lubrication), removal of metal debris produced by the work, reduction or inhibition of corrosion and prevention or reduction of build-up on edges as between the work piece and the tool. This combination of functions usually requires a formulation or combination of ingredients in the fluid to accomplish the best attributes required for a particular metal working operation.
Various fluids have been recently proposed to be substituted for oil-containing metal-working fluids such as primary amides, ethylenediamine tetraacetic acid, fatty acid esters, and alkanolamine salts. Such compounds can be replenished during use by dissolving tablets containing such compounds during the useful life of the fluid. See U.S. Pat. No. 4,144,188 to Sato.
Amines have also been found useful in cutting oils as antibacterial agents. Such amines include anilinoamines and arylalkylamine such a p-benxylaminophenol. See EPO 90-400732 to Noda et al.
As noted above, one of the problems occurring in industry is the proper disposal of metal working fluids. The above mentioned amines are removed from the fluids by biodegradation, requiring facilities such as settling tanks, treatment tanks and sludge treatment tanks. Such a system is disclosed in Japanese Patent 03181395. Other methods of waste disposal and oil removal systems are employed to comply with environmental standards.
Worker sanitation is always an issue with presently employed oil-containing water soluble metal- working fluids. Such fluids unavoidably come in contact with workers using the fluids in cutting, bending, threading and other metal-working applications. Such oil-containing fluids create a mist at the site of the work piece being operated on and such mist travels through the air in the vicinity of the machine and the operator thereof. Some attempts have been made to reduce the mist problem as is noted in British Patent 2,252,103. There is disclosed therein a polymeric thickener comprising a copolymer of acrylamide, sodium acrylate and N-n-octyl acrylamide. The copolymer is formulated with water soluble and water insoluble monomer.
Because of the misting and drift thereof in the work place employing the commonly employed water-soluble metal-working fluids, there is usually associated with such work place a distinctive odor which permeates the entire area. Usually such odor is unpleasant and is tolerated as a condition which is unavoidable.
There is needed a highly biodegradable, odorless, non-misting, water soluble metal working fluid, particularly useful in cutting operations. Such a fluid would dispense with the need for disposal costs, and provide the work place with a more sanitary and acceptable atmosphere in which to work.
Various methods have been discovered to catalyze the polymerization of a dry mixture of aspartic acid to form polysuccinimide. The preferred catalyst to perform in the dry environment is phosphoric acid. While phosphoric acid has been known for many years to be an excellent catalyst for the thermal condensation of aspartic acid, it has traditionally been employed in large quantities so as to form a liquid or pasty mixture. However the use of relatively small amounts so as to maintain a substantially flowable powder is also known. For example, it is disclosed in U.S. Pat. No. 5,142,062 to Knebel et al., that a weight ratio of aspartic/catalyst ratio in the range of from 1:0.1 to 1:2, can be employed. Also, Fox and Harada has published processes for thermal polycondensation of .beta.-amino acids in a publication entitled "Analytical Methods of Protein Chemistry" wherein a procedure is described employing a mole ratio of aspartic/catalyst of 1:0.07. Also, Fox and Harada disclose the use of polyphosphoric acid as a very effective catalyst for the polycondensation reaction of amino acids and indicate that temperatures below that required when o-phosphoric acid is employed are possible.